Benzoxazine compounds are cured when heated without generating volatile by-products. Further, they exhibit excellent properties such as heat resistance, flame retardance and electrical characteristics. Thus, the compounds are used in a wide variety of applications including laminated sheets, adhesives, electronic materials such as sealants, and complexes with carbon fibers, namely, prepregs. Further, benzoxazine compounds attract attention as alternative shaping materials to replace phenolic resins and epoxy resins.
The benzoxazine compounds may be easily synthesized from a phenol, an amine and an aqueous paraformaldehyde or formaldehyde solution as materials. A number of syntheses have been reported (for example, Patent Literatures 1 to 3).
However, the benzoxazine compounds with excellent heat resistance have problems in that because of their high crystallinity, the compounds are poor in solubility with respect to low-boiling solvents and are precipitated during a long storage at a low temperature. Further, because many of the benzoxazine compounds are prepared from aniline as the main material, insufficient heat resistance arises from the removal of aniline during curing.